1. Field of the Invention
In its fullest application, this invention pertains to circuits which can be used with Hall generators in order to make their outputs at least partially independent of variations in temperature and of differences in serial spread of characteristics of individual Hall generators. However, in its most immediate sense, this invention pertains to devices which perform these functions within a commutatorless motor in which a Hall generator is used to regulate current in the stator coil or coils as a function of rotor position.
2. Description of the Prior Art
It is known that the ouput of a Hall generator can vary depending upon factors such as temperature and differences in serial spread of characteristics of individual Hall generators. Particularly in commutatorless motors in which Hall generators are conventionally used in order to sense the direction of the magnetic field to allow electronic commutation to take place, variation in output can cause excessively large currents to flow and can thereby either reduce the working efficiency of the motor or lead to a destruction of components therein.
It is known from U.S. Pat. No. 4,134,030 to equip a Hall generator with auxiliary circuitry in a single monolithic chip in order to prevent such voltage changes from taking place. In this reference, a differential amplifier and current mirror circuit are coupled to the Hall generator and vary the threshold voltage of the differential amplifier in accordance with the output voltage of the Hall generator irrespective of current changes in the Hall generator due to temperature variations. While this reference pertains to the similar problems as those with which the invention herein is concerned, the problems are solved not by provision of additional circuitry outside the Hall generator chip but rather within the chip itself. It is a similar problem whereby not only the threshold but also the entire analogous range is compensated.
However, Hall generators without the extra circuitry disclosed in this reference are currently available and in use, and it would be desirable to provide an improvement for use with a conventional Hall generator which would at least partially compensate for changes in its output voltage which result from the above-mentioned causes. Such an improvement would enable a user to purchase conventional Hall generators and utilize them in, e.g., a commutatorless motor.